TinyPNG - Make your website faster and save bandwidth. TinyPNG optimizes your PNG images by 50-80% while preserving full transparency!
FILEminimizer Pictures - FILEminimizer Pictures compresses JPEG photos, TIFF, BMP and PNG images and pictures by up to 98%.
Optimus.io - Lossless image optimization
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.
OptiMole - Optimole makes your images weigh even 80% less while looking just as good!
DVDVideoSoft Image Convert and Resize - Free Image Convert and Resize is a compact yet powerful program for batch mode image processing.